There are multiple reports of this, with the solution indicated to delete and re add your account settings to get the folders to sync . This is not a solution because although it will work, subsequent syncing fails again. It's not plausible to constantly be adding your account. This is an issue that was introduced with a recent update. Please revisit.
The K9 option is not really valid either as that 3rd party app is not supported. Outlook on Android is a joke. I guess I could go with Gmail but I'm not a fan of that app on my phone.